A cutting insert mounted on a milling cutting tool for performing a high-speed process generally receives a considerable amount of cutting load during a cutting process. Accordingly, it is critical for the cutting insert used in the milling cutting tool to be reliably secured to the cutting tool body even under such a cutting load.
Generally, the cutting tool body includes a pocket part wherein the cutting insert is mounted. Said pocket part consists of a bottom surface and two planar side surfaces. The cutting insert is provided with a through-hole, through which the cutting insert is secured to the pocket part using a screw. Further, a lower surface and a side surface of said cutting insert contact a bottom surface and a side surface of the pocket part, wherein the cutting insert is pressurized and supported.
However, the bottom and side surfaces of the pocket part are not structured to provide any support to the cutting insert against the cutting load applied in the outward direction of the main body of the milling tool. This allows said cutting load to be transferred directly to the cutting insert, eventually applying an excessive force onto a screw and possibly causing damage to the screw. To lower the chances of damage, the cutting transfer speed and the cutting depth must be limited.
In order to solve such a problem, as shown in FIG. 1, there has been introduced a technique of forming projections (40) in the teeth shape on the lower surface (20) of the cutting insert (10) and grooves for receiving such projections on the bottom surface of the pocket part of the main body where the cutting insert (10) sits in. The cutting insert may be supported by the projections and the grooves, which provide the cutting insert with good resistance against the cutting load exerted in the outward direction of the main body of the tool. As such, the problem of the prior art can be resolved while ensuring a reliable fixing of the cutting insert to the main body.
However, the cutting insert should be configured such that the side and lower surfaces of the cutting insert contact the side and bottom surfaces of the pocket part of the main body. Further, it should also be configured such that the teeth-shaped projections of the cutting insert precisely fit in the grooves of the main body of the pocket part. Accordingly, the side and lower surfaces of the cutting insert and the pocket part must be produced in a precise manner. However, this inevitably increases manufacturing costs.
FIG. 2 illustrates another conventional cutting insert (50). The lower surface (55) of the cutting insert (50) is provided with concaves (60) in a V-shape. However, since it is difficult to polish the lower surface (55) due to its geometrical structure, the lower surface cannot be brought to a precise process. This causes the lower surface (55) not to precisely contact the bottom surface of the pocket part, thus failing to stably secure the cutting insert. Moreover, a super alloy cutting insert generally tends to be weak against a tensioning force but strong against a compressing force. Thus, in a structure providing concaves (60) to the lower surface (55) of the cutting insert, a predetermined opposing force to the pressuring force provided by the screw is generated at the projections (65) of the bottom surface of the pocket part, wherein said opposing force is applied to the cutting insert as the tensioning force. This can result in creating cracks around the concaves (60).
FIG. 3 illustrates yet another example of a conventional cutting insert (70). The lower surface (75) of the cutting insert (70) is provided with projections (80) on a portion of said lower surface. Further, the bottom surface of the pocket part is provided with concaves (85) receiving the projections (80). However, a gap is formed between the lower surface (90) and the bottom surface (75) of the pocket part. Accordingly, an excessive force may be applied to the screw during screw-fastening for securing the cutting insert to the bottom surface of the pocket part, which can damage the screw. In addition, from the concaves of the pocket part, the projections receive a predetermined opposing force to the cutting load, wherein said force is applied in the outward direction of the main body of the tool, thus ultimately damaging the projections.